[PATCH 6/6] KVM: x86: Expose Architectural LBR CPUID and its XSAVES bit

[Like Xu <like.xu@xxxxxxxxxxxxxxx>]

If CPUID.(EAX=07H, ECX=0):EDX[19] is exposed to 1, the KVM supports Arch
LBRs and CPUID leaf 01CH indicates details of the Arch LBRs capabilities.
As the first step, KVM only exposes the current LBR depth on the host for
guest, which is likely to be the maximum supported value on the host.

If KVM supports XSAVES, the CPUID.(EAX=0DH, ECX=1):EDX:ECX[bit 15]
is also exposed to 1, which means the availability of support for Arch
LBR configuration state save and restore. When available, guest software
operating at CPL=0 can use XSAVES/XRSTORS manage supervisor state
component Arch LBR for own purposes once IA32_XSS [bit 15] is set.
XSAVE support for Arch LBRs is enumerated in CPUID.(EAX=0DH, ECX=0FH).

Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/cpuid.c   | 19 +++++++++++++++++++
 arch/x86/kvm/vmx/vmx.c |  2 ++
 arch/x86/kvm/x86.c     |  6 ++++++
 3 files changed, 27 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 7d92854082a1..578ef0719182 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -713,6 +713,25 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			entry->edx = 0;
 		}
 		break;
+	/* Architectural LBR */
+	case 0x1c:
+	{
+		u64 lbr_depth_mask = 0;
+
+		if (!kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR)) {
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+			break;
+		}
+
+		lbr_depth_mask = 1UL << fls(entry->eax & 0xff);
+		/*
+		 * KVM only exposes the maximum supported depth,
+		 * which is also the value used by the host Arch LBR driver.
+		 */
+		entry->eax &= ~0xff;
+		entry->eax |= lbr_depth_mask;
+		break;
+	}
 	/* Intel PT */
 	case 0x14:
 		if (!kvm_cpu_cap_has(X86_FEATURE_INTEL_PT)) {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 3843aebf4efb..98bad0dbfdf1 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7409,6 +7409,8 @@ static __init void vmx_set_cpu_caps(void)
 		kvm_cpu_cap_check_and_set(X86_FEATURE_INVPCID);
 	if (vmx_pt_mode_is_host_guest())
 		kvm_cpu_cap_check_and_set(X86_FEATURE_INTEL_PT);
+	if (cpu_has_vmx_arch_lbr())
+		kvm_cpu_cap_check_and_set(X86_FEATURE_ARCH_LBR);
 
 	if (vmx_umip_emulated())
 		kvm_cpu_cap_set(X86_FEATURE_UMIP);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8a58d0355a99..4da3f9ee96a6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -184,6 +184,8 @@ static struct kvm_shared_msrs __percpu *shared_msrs;
 				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
 				| XFEATURE_MASK_PKRU)
 
+#define KVM_SUPPORTED_XSS_ARCH_LBR  (1ULL << 15)
+
 u64 __read_mostly host_efer;
 EXPORT_SYMBOL_GPL(host_efer);
 
@@ -9803,6 +9805,10 @@ int kvm_arch_hardware_setup(void *opaque)
 
 	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
 		supported_xss = 0;
+	else {
+		if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR))
+			supported_xss |= KVM_SUPPORTED_XSS_ARCH_LBR;
+	}
 
 #define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f)
 	cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_);
-- 
2.21.3